This invention generally relates to a method and device for accurately feeding discrete quantities of finely divided particulate matter and in particular is directed to such methods and devices in association with a gas-solids containing apparatus.
Many methods and devices are known for feeding pulverulent material in discrete quantities in cyclical manner. Volumetric mechanical devices are usually adequate from the standpoint of consistently feeding or discharging the same quantity of particulate material, but the wear and tear, due to the abrasive nature of many finely divided materials, renders the maintenance of such devices both difficult and expensive. Feeding devices which involve fluidizing the finely divided material avoid much of the abrasion problems characteristic of the mechanical devices, but such devices normally are not capable of consistently providing the same quantity of discrete amounts of pulverulent material in a cyclical manner.
In the operation of gas-solids contacting apparatus, such as fluidized beds, heat exchangers, gas-solids reactors, gas scrubbers and the like, the accurate feeding or discharging of particulate matter to or from the apparatus is quite important to control the process within the apparatus. Most gas-solids contacting devices are operated under a positive pressure which makes the introduction or removal of discrete quantities of particulate matter very difficult without excessive pressure drop. High pressure drops can increase the operational cost of such a process and can cause loss of particulate matter into the surrounding environment. The latter point can be critical if the particulate matter is a hazardous substance.
A feeding device is described in U.S. Pat. No. 3,411,666 wherein particulate matter is fed to a fluidizing container and fluidizing gas is introduced in a controlled manner so that the amount of fluidized particulate matter fed over the edge of the container is controlled in a desired manner. The device can feed discrete quantities of particulate matter in a repetitive manner, but the accuracy of the feeding device is not adequate for many purposes. Moreover, the device is ineffective in feeding particulate matter to a gas-solids contacting apparatus where such units would provide significant back pressure on the feeding unit.
It is against this background that the present invention was developed.